1. Field of the Invention
The present invention relates generally to an actuator which employs an electric power source as a driving power source and a position encoder for detecting an actuator position for stopping operation of the actuator at a desired position. More specifically, the invention relates to a motor-operated actuator which is suitable for use in a variable damping-characteristics shock absorber, such as a shock absorber in an automotive suspension system.
2. Description of the Background Art
In the automotive technologies, a requirement for variable damping force shock absorbers is increasing for providing variable suspension characteristics in order to achieve both driving stability and riding comfort of the vehicle. For answering this requirement, various constructions of variable damping-characteristics shock absorbers have been developed and put into the market. Some of the suspension systems employing such variable damping-characteristics shock absorbers employ automatic control strategies for automatically adjusting suspension characteristics according to the vehicular driving condition, or, in the alternative, for a remote control strategy for permitting adjustment of suspension characteristics through a manually operable switch arranged in the vehicular cabin. In order to allow automatic or remote control of the damping characteristics of the shock absorber, actuators are to be employed in the shock absorber.
For example, Japanese Utility Model First (unexamined) Publication No. 62-200829, published on Dec. 21, 1987 discloses one type of variable damping characteristics shock absorber employing a rotary valve for adjusting fluid flow restriction and thus adjusting damping characteristics of the shock absorber. In order to drive the rotary valve, a motor operated actuator is employed in the shock absorber. The actuator is associated with a position encoder for detecting the position of the actuator and stopping the motor at a desired position. The position encoder comprises an electrically conductive element with a plurality of circumferentially arranged brush contactors with a predetermined circumferential interval for detecting the angular position of the actuator corresponding to the position of the contactor. In such prior art actuator, a relatively wide transverse space lateral to the longitudinal axis of the shock absorber is required in order to circumferentially arrange the brush contactors.
This clearly prevent the shock absorber from being made more compact.